1. Field of the Invention
The present invention relates to an inkjet coating apparatus, and particularly to an on-demand inkjet coating method and apparatus suitable.
2. Description of the Related Art
A multi-nozzle inkjet coating apparatus can apply ink rapidly and densely over a workpiece (substrate) using an on-demand coating head that includes a dense arrangement of several hundred to several thousand nozzles. However, since the weight and ejection position of the ink droplets varies from nozzle to nozzle, this conventional multi-nozzle inkjet coating apparatus cannot form an even coating with precision and edges with sufficient precision.
The technology disclosed in Japanese unexamined patent application publication No. HEI-9-11457 achieves a uniform weight in ink droplets by fine-tuning individual drive voltage waveforms impressed on the piezoelectric elements and heating elements of each nozzle. However, while this technology can suppress variations in droplet weight, it has difficulty suppressing variations in ejection position and hence, the coating precision remains insufficient. Further, the technology cannot form edges with precision.
A leveling technology well known in the art can achieve a uniform expansion of ink droplets on the substrate by adjusting the viscosity of the ink and the angle at which the ink droplets contact the substrate. This technology can average variations in the weight and ejection position of ink droplets, thereby forming a uniform coating with precision. However, this precision drops when coating such detailed areas as edges. For example, ink droplets to form sharp corner will expand to form a rounded corner.
To overcome this problem, Japan unexamined patent application publication No. 2000-353594 proposes to control the direction of ink spreading by forming a banks at outer of edges with polyimide or the like and treating the surface of the bank to repel ink. With this method, edges can be formed with precision.
However, the method disclosed in Japan unexamined patent application publication No. 2000-353594 is generally complex and, therefore, the simplistic feature of the inkjet coating apparatus is lost. Moreover, the method is less cost-effective.
Further, a technology is disclosed in Japanese unexamined patent application publication No. HEI-5-278221 for increasing the optical density of edge parts at which ink droplets penetrate paper to form sharper images by ejecting ink droplets of a larger volume in the edge parts of an image and a smaller volume in non-edge parts.
However, Japanese unexamined patent application publication No HEI-5-278221 uses a plurality of nozzles to eject ink droplets in edge parts. Although this is not a problem if the nozzles precision is high, sharp edge parts cannot be formed if this precision is low. For example, when forming a side corresponding to an edge part if the precision of each nozzle is poor, the result will be a jagged side which is formed the plurality of nozzles.